This invention relates to a mixing rotor for mixing polymeric materials such as plastic materials and rubbers, and a mixer having such a rotor.
A closed batch mixer suitable for kneading rubber has been known as a mixer of this type, for example, in Japanese Examined Patent Publication No. 58-4567. This mixer is designed to plasticize and melt a material to be mixed such as a plastic material or rubber by applying a strong shearing action to the material to be mixed by means of a pair of right and left rotors rotating in different directions in a mixing chamber. By efficiently mixing and dispersing various fillers and additives into the material to be mixed, plastic and rubber products of various qualities can be produced.
FIGS. 4A to 4C show mixing rotors used in such a mixer. Each mixing rotor 4 is provided on its outer circumferential surface with longer blades 22 and shorter blades 23 for allowing a material to be mixed to pass through tip clearances between the tips of the blades 22, 23 and the inner surface of a mixing chamber and imparting shearing forces thereto.
For creating axial material flows 24, 24xe2x80x2 within the mixing chamber and thereby enhancing the degree of mixing of the material to be mixed, the longer and shorter blades 22, 23 are axially separated from each other, located at circumferentially displaced positions, and twisted in opposite directions.
In the conventional mixing rotor 4 as above, the respective blades 22, 23 are all linear in a development of the mixing rotor 4 developed into a plane about its longitudinal axis, and helix angles xcex8 thereof are all the same. In other words, the helix angle xcex8 of each blade 22, 23 is constant in the range from a start point P to a terminal point Q. In FIG. 4, the letter xe2x80x9crxe2x80x9d denotes a rotational direction of the mixing rotor. Similarly, the letter xe2x80x9crxe2x80x9d denotes a rotational direction of a mixing rotor in the drawings showing an embodiment to be described later.
By increasing the helix angles xcex8 of the blades 22, 23 to the axial direction, an axial feed capacity is improved to thereby enhance the degree of mixing of the material to be mixed. Conversely, by decreasing the helix angles xcex8, a passage quantity of the material to be mixed through the tip clearances (hereinafter referred to as xe2x80x9cmaterial passage quantityxe2x80x9d) increases to thereby enhance the degree of dispersion of the material to be mixed.
However, since the helix angle of each blade 22, 23 is constant in the range from the start point P to the terminal point Q, it has been difficult to balance the degree of mixing and the degree of dispersion of the material to be mixed. This has resulted in difficulty to execute an appropriate control for securing well-balanced mixing and dispersion of the material to be mixed.
For example, if the helix angle xcex8 is increased in the mixing rotor 4 for the batch mixer shown in FIG. 4 with the longer and shorter blades 22, 23 left linear in the development, the axial flows 24, 24xe2x80x2 of the material to be mixed become larger, making it possible to enhance the degree of mixing. In such a case, the material passage quantity through the tip clearances of the respective blades 22, 23 decreases, resulting in a reduced degree of dispersion.
Conversely, if the helix angle xcex8 is decreased with the longer and shorter blades left linear in the development, the material passage quantity through the tip clearances of the respective blades 22, 23 increases, making it possible to enhance the degree of dispersion. However, in such a case, the axial flows 24, 24xe2x80x2 of the material to be mixed become smaller, resulting in a reduced degree of mixing.
It is an object of the present invention to provide a batch mixer and a mixing rotor which are free from the problems residing in the prior art.
It is another object of the present invention to provide an appropriate mixing control capable of realizing both sufficient mixing and sufficient dispersion of a material to be mixed by efficiently balancing mixing and dispersion of the material by means of mixing rotors.
According to an aspect of the present invention, a batch mixer is rotatably provided with a mixing rotor in a mixing chamber of the mixer. The mixing rotor comprises a plurality of mixing blades, each mixing blade defining a tip clearance between a tip of the mixing blade and an inner surface of the mixing chamber. The mixing blade imparts shearing forces to a material to be mixed in the tip clearance. The plurality of mixing blades includes a nonlinear blade which is substantially nonlinear from a start point to a terminal point in a development of the mixing rotor developed into a plane about its longitudinal axis, and other linear blades which is linear in the development.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.